Timekeeping devices have enabled users to know whether the hour indicated by an hour hand on a timepiece is in the first or second half of a day. The indication is typically performed by having two sets of hour indicia on the face of the dial, a first set illustrating hour indicia between 0:00 hours, (or mid-night), and 12:00 hours, (or noon), and second set illustrating hour indicia between 12:00 hours and 0:00 hours. However, the second set of hour indicia cannot be functionally used for operating a chronograph mode to displaying chronograph times since the user would not be able to properly discern which set of the first and second set of indicia is relevant to any chronograph time once an elapsed chronograph time is greater than 12 hours.
Another timepiece disclosed in U.S. Pat. No. 4,740,934 to Noirjean has hour and minute hands rotatably driven before a dial by a movement at the rate of one revolution every twelve hours and of one revolution every hour respectively. The dial is not provided with the traditional indicia that are typically used for designating hours but is formed with display apertures located where these indicia are normally located. A rotary disc, lying beneath the dial, bears two sets of indicia distributed along its periphery and is driven by a mechanism to move the rotary disc in the same direction such that the two sets of indicia are displayed through the display apertures.
A drawback from this type of invention is that the rotary disc bearing the two sets of indicia can only be actuated at limited and specific times of the day, thus creating an inability to spontaneously use a chronograph function on the timekeeping device in combination with the two sets of hour indicia. The embodiments described herein address this limitation in the prior art and provide the ability to instantly display a chronograph time using either of two sets of 12-hour sequential timekeeping periods and the ability to toggle between a timekeeping display mode and any number of chronographs display modes at any time and as many times as a user determines.